The invention relates to releasing a silicone-based pressure-sensitive adhesive composition from contact with a release liner after aging.
Silicone-based pressure-sensitive adhesive compositions are very versatile because they tend to exhibit good adhesion to a variety of substrates including glass, ceramic, vinyl siding, finished wood, and painted drywall under challenging environmental conditions including temperature and humidity extremes. Many silicone-based pressure-sensitive adhesive compositions are coated onto a release liner as a wet composition, dried and wound up into a roll. Providing the silicone-based pressure-sensitive adhesive on a release liner facilitates further processing of the adhesive including, e.g., transfer laminating, converting and packaging.
Release liners provide a variety of functions for pressure-sensitive adhesive compositions including, e.g., preventing contamination of the adhesive layer, facilitating handling of the adhesive or an adhesive-coated article (e.g., by providing support thereto as well as covering the adhesive), identifying articles on which the release liner is disposed and combinations thereof. A release liner is often left in place on a pressure-sensitive adhesive composition until the adhesive layer is converted, packaged, or shipped to ultimate users, and in many instances the release liner is left in place until the adhesive is adhered to another substrate. As a result, a pressure-sensitive adhesive coated release liner potentially may experience a variety of environmental conditions including changes in temperature and humidity and must be functional over extended periods of time.
The strength of the adhesive bond formed between a silicone-based pressure-sensitive adhesive composition and a release liner tends to increase over time and upon exposure to elevated temperatures. This phenomenon is referred to as “adhesion build.” If the strength of the bond between the adhesive composition and the release liner is too great, the release liner and the adhesive composition cannot be separated from each other or can be separated only with difficulty, rendering the adhesive unsuitable for its intended purpose or frustrating the user. For articles that include silicone-based pressure-sensitive adhesive compositions, an undesirable degree of adhesion build often occurs before the end of the useful life of the article thereby effectively decreasing the useful life of the article.
A number of attempts have been made to decrease the degree of adhesion build between an adhesive and a liner. One useful method involves altering the surface chemistry of the liner by coating the liner with a surface chemistry modifier. Fluorosilicones are a common class of surface chemistry modifiers that have been coated on liners to improve their release properties. Although some of these methods have reduced the adhesion level, adhesion build continues to occur and the rate of adhesion build remains undesirable. It would be desirable to achieve a silicone-based pressure-sensitive adhesive article that includes a silicone-based pressure-sensitive adhesive composition in contact with a release liner and that can be stored for an extended period of time and exhibit a sufficiently low adhesion build such that the adhesive composition releases cleanly and relatively easily from the release liner. It also would be desirable to achieve a stretch releasing pressure-sensitive adhesive article that can be stored for an extended period of time and exhibit a sufficiently low adhesion build to the release liner such that the adhesive composition releases cleanly and relatively easily from the release liner.
Pressure-sensitive adhesive articles that are removable from a substrate through stretching are often referred to as stretch releasing pressure-sensitive adhesive articles. A number of backed and un-backed stretch releasing pressure-sensitive adhesive articles are described in literature and in patents. U.S. Pat. No. 4,024,312 (Korpman), for example, discloses a highly conformable adhesive article that includes a highly extensible and elastic backing film laminated with an adhesive layer. The adhesive article is easily stretchable and may be removed from a surface by stretching the article lengthwise in a direction substantially parallel to the surface. German Patent No. 33 31 016 discloses a high elasticity, low plasticity adhesive film based on a thermoplastic rubber and tackifying resins in which the adhesive bond can be broken by stretching the adhesive film in the direction of the plane of the adhesive bond. U.S. Pat. No. 5,516,581 (Kreckel et al.) discloses a removable adhesive article having a highly extensible and substantially inelastic backing coated with a layer of pressure-sensitive adhesive and a non-adhesive pull tab to facilitate stretch removal. The adhesive article can be removed from most surfaces without damaging the substrate by grasping the non-adhesive pull tab and stretching the article in a direction substantially parallel to the surface of the substrate. U.S. Pat. No. 6,231,962 (Bries et al.) discloses a removable foam adhesive strip that includes a backing that includes a layer of polymeric foam and a pressure-sensitive adhesive layer coated on at least one surface of the backing. A commercially available stretch releasing adhesive article is sold under the trade designation COMMAND by 3M Company, St. Paul, Minn.